Total mercury concentrations in coastal areas of Thailand: A review

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Abstract
Thailand has recognized mercury (Hg) as one of the most hazardous metals and considers this metal as a national concern. This article reviews the existing data on the total mercury concentrations in seawater, sediments and marine organisms in coastal areas of Thailand beginning in 1974 to 1999. The purpose of this article is to assess the degree of mercury contamination in Thai coastal environments. The mercury standards/guidelines from both Thailand and other countries are also included. In general, the situation of mercury contamination in Thai coastal areas is still within a safe level, except a few samples exceeding the standard have been collected in some areas.
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Total Mercury Concentrations
in Coastal Areas of Thailand: A Review
Waewtaa Thongra-ara,* and Preeda Parkpianb
IaInstitute of Marine Science, Burapha University, Bangsaen, Chonburi 20131, Thailand.
bSchool of Environment, Resources and Development, Asian Institute of Technology, PO Box 4,
Klongluang, Pathumthani 12120 Thailand.
Corresponding author, E-mail: waewtaa@bucc4.buu.ac.th
Received 18 Jan 2002
Accepted 7 May 2002
ABSTRACT Thailand has recognized mercury (Hg) as one of the most hazardous metals and considers
this metal as a national concern. This article reviews the existing data on the total mercury concentrations
in seawater, sediments and marine organisms in coastal areas of Thailand beginning in 1974 to 1999.
The purpose of this article is to assess the degree of mercury contamination in Thai coastal environments.
The mercury standards/guidelines from both Thailand and other countries are also included. In general,
the situation of mercury contamination in Thai coastal areas is still within a safe level, except a few
samples exceeding the standard have been collected in some areas.
KEYWORDS: mercury, seawater, sediment, marine organisms, coastal area.
ScienceAsia 28 (2002) : 301-312
INTRODUCTION
Thailand is situated in the tropical moonsoon
belt of Southeast Asia. The country is bounded in
the north, west and east by mountain ranges and
in the south by the South China Sea and the
Andaman Sea, with a total coastline of approximately
2,600 kilometers. The Gulf of Thailand (Fig 1) is
an enclosed sea in the southwestern part of the
South China Sea, covering an area of approximately
350,000 km2, with an average water depth of 55
meters and a maximum of 84 meters. The Gulf is
divided into two portions: the Upper Gulf and Lower
Gulf. The Upper Gulf located at the innermost area
is an inverted-U shape1, which has a coastline of 700
kilometers from Prachaub-Kiri-Khan Province to
Rayong Province.2 The Upper Gulf is very shallow
with an average depth of 15 meters, whereas the
Lower Gulf includes a relatively deep part with an
average depth of 55 meters.1 In coastal areas, many
developments with high rates of industrialization
and urbanization have taken place, thereby changing
the landuse pattern and deteriorating natural
resources and the aquatic environment. Numerous
industries located along the coast discharge their
wastes into the Upper Gulf causing water quality
deterioration with major pollutants from organic
wastes. In some locations, the Upper Gulf has been
faced the problems from heavy metals (including
mercury) discharged by industries.2 In particular,
Map Ta Phut Industrial Estate established in 1989
in Rayong Province along the east coast has developed
as a national heavy metal center, including a gas
separation plant, oil refineries and petrochemical and
chemical plants. Laem Chabang Industrial Estate
was established in 1987 in Chonburi Province for
medium-sized and non-polluting industries with
Fig 1. Map showing the Gulf of Thailand.
302 ScienceAsia 28 (2002)
three petroleum refineries being located nearby the
Estate. In addition, there has been an increase in
the number of platforms for oil and gas exploration
and production in the Gulf of Thailand.3 The water
quality deterioration in the Upper Gulf is partly
due to wastes from the rivers because there are four
major rivers draining into the Upper Gulf, namely
the Chao Phraya, the Mae Klong, the Ta Chin and
the Bangpakong Rivers.
Mercury is recognized as one of the most toxic
pollutants in the coastal environment and is a
national pollutant in Thailand. Mercury and its
compounds are widely used in a variety of industrial
and agricultural applications. Thailand has further
developed with a rapid expansion of industrialization,
urbanization and use of pesticides in agriculture
anticipated. These activities will substantially
increase the degree of heavy metal pollution, which
will subsequently have a direct impact on the quality
of life of the people in the coastal areas.
Here the existing data on the total mercury
concentrations in seawater, sediments and marine
organisms in coastal areas of Thailand are reviewed.
The data are taken from various studies undertaken
by government and private agencies available since
1974, in order to document the past and present
status of mercury contamination in Thai coastal
environments.
MERCURY CONCENTRATIONS IN SEAWATER
Heavy metal monitoring in Thailand began more
than twenty years ago. There have been many studies
on heavy metal concentrations in seawater. However,
there are not many papers reporting studies of
mercury compared to other heavy metals during
the past twenty-five years. Considering the data
obtained from several reports beginning in 1974
(Table 1), it can be observed that higher mercury
concentrations in Thai coastal water were found in
the early period, especially from 1979 to 1986, than
in recent years. The highest mercury concentration
reported (386 µg L-1) was found in the areas of
Bangpakong to Bang Pra in 19814, whereas in the
Upper Gulf, a concentration of 342 µg L-1 was found
in 19795 and a concentration of 203 µg L-1 found
during 1983 to 19866. The high mercury concentra-
tions found in the past were probably due to some
errors in methodology, measurement and sample
collection. Utoomprurkporn et al7 discovered that
heavy metal concentrations in seawater reported for
the Gulf of Thailand were apparently decreasing by
as much as 500 times from 1979 to 1985, which is
likely due to improvement in analytical techniques
and methodology, rather than a decrease in the
discharge of heavy metals into the Gulf. This
improvement may account for the decrease in
mercury and other heavy metals concentrations
indicated in recent studies compared to previous
studies.1 Therefore, a decrease in mercury concentra-
tion has been observed since 1986. In general high
mercury concentrations are occasionally observed
in some coastal areas, however, the overall situation
is still within a safe level, except at some locations
and during some sampling periods as reported by
Chongprasith and Wilairatanadilok.3
Recently, Thailand has faced the problem of
increasing mercury concentrations in the coastal
areas as a result of industrial activities and also in
the Gulf due to oil and gas activities. Chongprasith
and Wilairatanadilok3 reported that total mercury
in coastal waters has been monitored along the
entire Thailand coastline by the Pollution Control
Department since 1997, covering 218 sampling sites.
Specific areas, such as industrial estates in Map Ta
Phut and Laem Chabang, where elevated mercury
concentrations were found have been monitored
more extensively. The results showed that mercury
concentrations ranged from <0.01 to 0.54 µg L-1 with
an average of 0.032 µg L-1 during the periods from
1997 to 1998; mostly in compliance with the
National Coastal Water Quality Standard for mercury
of 0.1 µg L-1. They also reported total mercury
concentrations found in the areas adjacent to the
Map Ta Phut Industrial Estate and the Laem Chabang
Industrial Estate. Results of the mercury con-
centrations in the area from the former location
ranged from 0.01 to 0.48 µg L-1 with an average of
0.057 µg L-1 during the periods from 1995 to 1998
whereas those from the latter ranged from <0.01 to
0.16 µg L-1 with an average of 0.064 µg L-1during
the periods from 1995 to 1996. High mercury
concentrations were detected in the Map Ta Phut
area especially in 1995-1996. They also reported
high mercury concentrations in the areas around
natural gas platforms and in the inner Gulf of
Thailand ranging from <0.01 to 0.51 µg L-1 during
the periods from 1995 to 1998 with a peak in 1995,
then decreasing in the following years. This was
possibly due to the release of mercury from dis-
charged water produced from oil and gas activities.
In addition, results reported by EVS Environment
Consultants8 showed that mercury concentrations
in the Gulf of Thailand and around the Industrial
Estates on the east coast in 1998 were below the
National Coastal Water Quality Standard for mercury
ScienceAsia 28 (2002) 303
Table 1. Total mercury in water and sediments in coastal areas of Thailand.
Study Total Mercury
Period Location Water (µg L-1) Sediment (µg g-1 dry wt) Reference
Gulf of Thailand
1975-1976 Upper Gulf 0.01 - 0.11 - 9
1977 Upper Gulf 0.02 - 2.00 - 9
1975-1976 Upper Gulf 0.467 - 10
1979 Upper Gulf 1.54 - 12.0 0.049 - 0.268 11
1981 Upper Gulf nil - 1.58 nil - 0.28 4
1982 Upper Gulf nil - 0.40 0.01 - 0.26
1978 Upper Gulf 0.01 - 0.29 0.1 - 0.13 5
1979 Upper Gulf 0.27 - 342 0.0 - 0.24
1980 Upper Gulf 0.2 - 1.0 0.0 - 1.2
1981 Upper Gulf 0.25 - 4.25 0.01 - 0.14
1983-1986 Upper Gulf 0.2 - 203.0 - 6
1995-1998 Gulf of Thailand (Natural gas < 0.01 - 0.51 0.006 - 0.121 3
platforms and in the inner Gulf) (0.046)
1998 Gulf of Thailand ND - 3.000 0.05 - 2.8 8
River Mouths and Coastal Areas
1974 Bang Pra Coast Chonburi 0.015 - 0.019 0.003 - 0.069 (wet wt) 12
1976 Chao Phraya Estuary 0.216 ± 0.280 0.012 - 0.264 13
1978-1979 Estuarine areas 11
- Mae Klong 0.12 - 10.10 0.036 - 0.885
- Ta Chin 0.12 - 6.40 0.071 - 0.746
- Chao Phraya 0.94 - 8.20 0.079 - 1.860
- Bangpakong 0.55 - 12.96 0.069 - 0.299
1980 Estuarine areas 14
- Mae Klong 0.03 -
- Ta Chin 0.25 -
- Chao Phraya 0.74 -
- Bangpakong 0.30 -
1980 Estuarine areas 15
- Mae Klong - 0.23 ± 0.1
- Ta Chin - 0.67 ± 0.1
- Chao Phraya - 2.80 ± 0.4
- Bangpakong - 0.52 ± 0.2
1981 Bangpakong Estuary to Bang Pra nil - 386 nil - 0.80 4
1977-1981 Bangpakong Estuary 4.60 - 16
Ang Sila 6.50 -
Bang Saen 16.30 -
Bang Pra 2.10 -
Si Racha 1.30 ± 6.20 -
Pattaya 0.35 ± 0.54 -
1979-1980 Estuarine areas 17
- Bangpakong 0.10 - 1.22 0.000 - 0.038
(0.30 ± 0.20) (0.014 ± 0.014)
- Mae Klong 0.08 - 1.25 0.006 - 0.046
(0.38 ± 0.30) (0.014 ± 0.011)
- Ta Chin 0.10 - 0.50 0.006 - 0.038
(0.24 ± 0.09) (0.017 ± 0.009)
- Petchburi 0.08 - 0.88 0.004 - 0.015
(0.27 ± 0.19) (0.007 ± 0.044)
- Pranburi 0.08 - 0.82 0.006 - 0.038
(0.28 ± 0.17) (0.014 ± 0.011)
304 ScienceAsia 28 (2002)
Table 1. Cont'd.
Study Total Mercury
Period Location Water (µg L-1) Sediment (µg g-1 dry wt) Reference
1992-1993 Bangpakong River 0.10 - 0.12 - 18
1983-1984 East Coast of the nil - 85 0.01 - 0.14 19
Upper Gulf
1987-1990 Aquaculture areas 20
- Bangpakong River mouth < 0.2 - 0.6 -
to Ang Sila
- Chantaburi toTrat < 0.2 - 0.5 -
1987-1988 - Bangpakong River - 0.1 - 1.5 20
mouth to Ang Sila
- Chantaburi toTrat - 0.1 - 1.2
1990 Ban Phe Bay, Rayong 0.0006 - 0.0024 - 21
(0.0015)
1992-1993 Aquaculture areas 22
- Bangpakong River ND - 0.48 -
mouth to Ang Sila
1992 Coast of Trat 0.0006 - 0.0448 - 23
(0.014)
1993 East Coast (Chonburi-Trat) 0.02 - 24
1994 East Coast (Chonburi-Trat) ND - 0.0861 - 25
(0.0188)
1995 East Coast (Chonburi-Trat) < 0.001 - 0.096 - 26
June 1997- Entire Coast of the Gulf of < 0.01 - 0.54 - 3
July 1998 Thailand and the Andaman Sea (0.032)
March -April 1998 Entire Coast of the Gulf of - 0.047 - 2.135 3
Thailand and the Andaman Sea (0.136)
March 1999 Bangpakong River Estuary - 0.12 - 0.48 27
(0-10 cm depth)
Industrial Estate
Petrochemical Complex site, 0.3 - 22.0 0.0262 - 0.2845 28
Chonburi (5.58 ± 5.23)
1977-1981 Map Ta Phut 0.60 ± 0.20 - 16
1987-1990 Industrial areas 29
- Laem Chabang <0.2 - 0.7 -
- Map Ta Phut <0.2 - 0.8 -
1987-1988 - Laem Chabang - 0.1 - 1.4 29
- Map Ta Phut - ND - 1.2
1992-1993 Laem Chabang ND - 0.26 - 22
Map Ta Phut ND - 0.76 -
1995-1998 Map Ta Phut Industrial Estate, 0.01 - 0.48 <0.005 - 0.134 3
Rayong (0.057)
1995-1996 Laem Chabang Industrial Estate, <0.01 - 0.16 - 3
Chonburi (0.064)
1996-1998 Laem Chabang Industrial Estate, - <0.005 - 0.032 3
Chonburi (0.016)
April 1998 Laem Chabang - <0.005 - 0.139 8
Map Ta Phut 0.01 - 0.02 <0.005 - 0.037
June-July 1998 Laem Chabang 0.01 - 0.02 0.024 - 0.037
Map Ta Phut 0.01 - 0.03 <0.005 - 0.156 8
Standard/Guideline
Canadian Water Quality Guideline for Protection 0.1 - 30
of Aquatic Life
World Average Value for Seawater 0.05 - 31
Thai Water Quality Criteria for Protection of 0.5 - 20
Freshwater Animals
ScienceAsia 28 (2002) 305
Table 1. Cont'd.
Study Total Mercury
Period Location Water (µg L-1) Sediment (µg g-1 dry wt) Reference
Thai Surface Water Quality Standard 2.0 - 20
Thai Coastal Water Quality Standard 0.1 - 20
ASEAN Marine Water Quality Criteria 32
- For protection of aquatic life 0.16 -
- For protection of human health from seafood 0.04 -
consumption
- For protection of human health from recreational 21 -
activities
World average value for marine sediment - 0.3 33
Clean ocean sediment - 0.1-1.0 34
Average shale - 0.4 35
Earth’s crust - 0.08 31
Average crustal abundance - 0.08 36
Sediment Quality Standard for the State of - 0.41 37
Washington
Draft Interim Canadian Marine Sediment - 0.13 38
Quality Guideline
Draft Interim Canadian Freshwater Sediment - 0.174 38
Quality Guideline
Sediment Quality Guidelines for
- Florida - 0.13 - 0.7 MacDonald
(1994) 8
- Australia and New Zealand - 0.15 - 1 ANZECC
(1998) 8
- Hong Kong - 0.5 - 1 HKGS
(1998) 8
ND = Non-detectable
of 0.1 µg L-1 (with the exception of only one sample
in the Gulf exceeding the standard), and the average
mercury concentrations appeared to be elevated
along the southern Gulf.
MERCURY CONCENTRATIONS IN SEDIMENTS
Sediment is considered to be a good indicator of
metal pollution because it serves as a source as well
as an ultimate sink of many pollutants in the aquatic
environment, thus providing the best assessment of
pollutant distribution. As a result, mercury in
sediments has received increasing attention in recent
years. From the existing data, there are two areas
found to have very high mercury contamination in
sediments (>1.0 µg g-1 dry weight). The first area is
the Upper Gulf particularly in the Chao Phraya area
in 1978-1979, as reported by Polprasert et al11, in
1980 reported by Menasveta and Cheevaparana-
piwat15 and in 1998 reported by EVS Environment
Consultants.8 Another area is near the industrial
estates of the east coast in 1987 reported by the
Pollution Control Department29 (see Table 1). A
decrease in sediment mercury concentrations was
observed in recent studies by Chongprasith and
Wilairatanadilok3 and EVS Environment Consultants8
compared to the early studies, especially near the
industrial estates of the east coast. However, the
concentrations detected in some stations were still
higher than some sediment quality standards. Since
Thailand does not have a sediment quality standard
at the present time, some sediment mercury
guidelines and standards of other countries and some
natural background values have been used to
evaluate the sediment mercury problem in Thailand.
Among various guidelines and standards, the lower
value of mercury is 0.13 µg g-1 dry weight belonging
to the Canadian Marine Sediment Quality Guideline
(interim draft )38 and the Sediment Quality Guideline
for Florida8 (Table 1). Also, there are two natural
background values of mercury: average shale value
(0.4 µg g-1 dry weight) of Turekian and Wedepohl 35
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